Respiratory activities in chloramphenicol-treated tobacco cells

Chloramphenicol (CAP) inhibited tobacco cell growth as shown by a reduction (34%) of cell mass 4 days after treatment, The rates of cell respiration w ere slightly higher than control under coupled conditions, However, CAP-tre ated cells showed a decreased maximal capacity of the cytochrome pathway (4 8%) and an increased maximal capacity. bl alternative path (56%) 4 days aft er treatment, in purified mitochondria, the rates of NADH or malate oxidati on under state 4 conditions were not significantly changed by CAP treatment , However, the state 3 rates were 33-40% lower in CAP-treated than in contr ol mitochondria, Succinate oxidation decreased by 31-46% under both state 4 and state 3 conditions after CAP treatment, The activities of complexes I, Iii, and IV, which contain mitochondrially encoded subunits, decreased by about 50% in CAP-treated mitochondria. There nas also a decrease in the con tents of mitochondrial cytochromes. Unexpectedly, the activities of complex II and the matrix-facing rotenone-in-sensitive NADH dehydrogenase, which a re thought to be nuclear-encoded, also declined, The activities of external NADH dehydrogenase, NAD-linked malic enzyme, and fumarase remained unchang ed after CAP treatment, There was a slight increase in the activity and pro tein level of alternative oxidase. An electrochemical gradient across the m itochondrial membranes Has observed by Rhodamine 123 staining in CAP-treate d cells. However, the morphology of most of the mitochondria changed from s pherical to vermicular. A method for purifying a high yield of intact mitoc hondria from tobacco cell suspension cultures is described.